1. Field of the Invention
The present invention relates to an inkjet recording apparatus for discharging ink onto a sheet serving as a recording material to record an image thereon. More particularly, the present invention relates to a structure of an ink receiver provided on a platen to receive ink discharged onto a border portion of a sheet serving as a recording material.
2. Description of the Related Art
In inkjet recording apparatuses, recording of an image without generating a margin at an end portion of a sheet (i.e., borderless recording) is realized by recording an image whose size is larger than that of the sheet. Thus, an ink receiver (i.e., a borderless recording groove) used exclusively for borderless-recording of an image is provided at a position corresponding to an edge of each area of a sheet size on a sheet supporting platen to prevent the platen from being stained by ink running off the sheet (see Japanese Patent Application Laid-Open No. 2006-231612). An inkjet recording apparatus is known, which is configured such that a hole for suctioning ink (i.e., a borderless recording groove suction hole) is provided in the borderless recording groove. The borderless recording groove suction hole assumes a role of attracting a sheet to the platen by generating a negative pressure.
It is known that in such an inkjet recording apparatus, an impact position of ink discharged in a vicinity of a sheet edge is shifted along a suction airflow under influence of a negative pressure generated when ink is suctioned by the borderless recording groove suction hole. In the inkjet recording apparatus, an image is formed by repetition of a set of a recording operation and a sheet-conveying operation. Due to the shift of the impact position of ink, a white streak (white dropout) is generated on a boundary part between recording areas (hereinafter referred to as record bands), each of which is recorded by a recording head at each single scan, on a sheet edge portion.
FIG. 14 is an enlarged view illustrating a configuration of a borderless recording groove 116 provided on a platen 102. As illustrated in FIG. 14, the center in a nozzle port arrangement direction of each nozzle row (discharge-port row) 119, which is arranged in a recording head 107 and is composed of a plurality of nozzles (discharge ports), is located on a straight-line L1 extending in a main scanning direction along which a carriage moves. A borderless recording groove suction hole 117 is provided on the straight-line L1. In the vicinity of a sheet edge, ink discharged from the nozzles of the nozzle row 119 is affected by an airflow generated due to suction by the borderless recording groove suction hole 117. Thus, as illustrated in FIG. 15, shift of the impact position of ink in each of directions respectively indicated by arrows towards the borderless recording groove suction hole 117 along the airflow is caused. Dashed-line circles (white circles) indicate ideal impact positions of ink. Filled circles (black circles) indicate actual impact positions of ink. FIGS. 16A through 16C are schematic views illustrating a mechanism of occurrence of a white streak by focusing attention on formation of a boundary part between record bands in a recording operation. As illustrated in FIG. 16A, ink discharged from the most-upstream one of nozzles of each nozzle row impacts at a position located on a line d2, which is shifted by a suction airflow from an ideal impact position located on a line d1. It is known that at that time, an amount of shift of the impact position in a sheet conveying direction (i.e., a distance between the lines d1 and d2) is 10 micro-meters (μm) if a volume flow rate of the airflow from the borderless recording groove suction hole 117 is 1×10−4 m3/seconds (s) and the diameter of each ink droplet is 20 μm. The larger the airflow, and the smaller the ink droplet, the larger the amount of shift of the impact position of ink.
Upon completion of an operation of recording one line, a sheet conveying operation is performed. Then, an operation of recording the next line is performed. As illustrated in FIG. 16B, an ink droplet discharged from the most-downstream one of nozzles of each nozzle row impacts at a position located on a line d4, which is shifted by a suction airflow from an ideal impact position located on a line d3. Accordingly, as illustrated in FIG. 16C, no ink impacts on a boundary part between the record bands. Thus, a white streak is generated thereon. That is, if a set of a recording operation and a sheet conveying operation is repeated, as illustrated in FIG. 17, an image is formed, in which a white streak S1 is generated in each boundary part between record bands in an associated recording operation. In addition, a white streak generated at each boundary part between record bands in the vicinity of the sheet edge can be more noticeable, depending upon variation of a sheet conveying operation.
The above problems occur when ink is discharged in the vicinity of the sheet edge, regardless of which of the borderless recording and bordered recording the inkjet recording apparatus performs. The mechanism of occurrence of a white streak has been described in the case of recording of each line by performing what is called single-pass feed of a sheet. However, even if each line is recorded by performing what is called multi-pass feed of a sheet, white streaks occur similarly. The amount of the shift of the impact position of ink due to the suction airflow can be reduced by lowering a suction force of suctioning air from the borderless recording groove suction hole. However, in this case, there is possibility of occurrence of other problems such as stain on the rear surface of a sheet due to record mist, sheet floatation due to reduction in the suction force, and clogging of the hole due to viscosified ink.